Tree harvesters are in extensive use to hold and cut trees and transport the harvested product to a desired location. Such tree harvesters commonly use a shear blade assembly which has two blade portions each with a cutting edge. The blade portions are urged into opposite sides of a tree in order to sever the trunk for harvesting purposes. The operation and details of such a tree harvester are shown, for example, in U.S. Pat. No. 3,797,539 which issued to Moser et al. on Mar. 19, 1974.
It has become increasingly common to form such shear blade assemblies in a concave, cylindrical or spherical configuration in order to minimize damage to the trees to be cut and to carry cutting loads through the assemblies in a more efficient manner. Such curved blades assemblies are disclosed in U.S. Pat. Nos. 4,069,847 which issued to Wirt on Jan. 24, 1978, and 4,131,145 which issued to Puna on Dec. 26, 1978, and also in Canadian Pat. No. 840,776 which was granted to Brundell and Jonsson AB on May 5, 1970.
Heretofore, such dish-shaped blade assemblies have been manufactured either by depressing a blank to a desired shape, dividing it into first and second portions and then machining cutting edges along the resultant curved edges or by individually making the first and second blade portions from separate pieces of flat plate. The latter method is disclosed briefly in U.S. Pat. No. 3,690,353 which issued to Johnston et al. on Sept. 12, 1972. Where the cutting edges are machined along the curved surfaces, special machining techniques are required to maintain a constant chamfer or beveled edge which is critical to the operation of the curved blades. Where the blade portions of the shear blade assembly are formed separately, there can be some problem with uniformity between portions, as well as duplicate manufacturing operations.
The present invention is directed to overcoming one or more of the problems as set forth above.